Hybrid deflection image dissector having concave deflection plates converging at horizontal edges of resolving apertures



March 11, 1969 H. CLAYTON 3,432,711

HYBRID DEFLECTION IMAGE DISSECTOR HAVING CONCAVE DEFLECTION PLATESCONVERGING AT HORIZONTAL EDGES 0F RESOLVING APERTURES Filed July 5, 1966adx l 32 Til i/ .9 J

INVENTOR.

R/l. CLAYTON BY W A TTORNEY United States Patent 3,432,711 HYBRIDDEFLECTION IMAGE DISSECTOR HAVING CON CAVE DEFLECTION PLATES CONVERGINGAT HORIZONTAL EDGES OF RESOLVING APERTURES Robert H. Clayton, FortWayne, Ind., assignor to International Telephone and TelegraphCorporation, Nutley, N.J., a corporation of Delaware Filed July 5, 1966,Ser. No. 562,773 US. Cl. 313-79 Int. Cl. H0lj 29/76 6 Claims ABSTRACT OFTHE DISCLOSURE This invention relates to a novel image dissector tubeand particularly to such a tube which utilizes a combination of magneticfocusing and electrostatic deflection for line scanning to provide amore compact structure with high resolution and fast response.

Image dissector tubes, providing an electrical signal representingsuccessively scanned areas of an image or scene of varying lightintensity, are being increasingly utilized for space surveillance andfor optical input information to computers. It is generally desirable toemploy magnetic focusing of the tube to obtain high resolution. However,the conventional accompanying magnetic deflection coils add excessiveweight and require high power for operation, so that an all magnetictube is not satisfactory for use in many instances. In addition,electrostatic deflection provides faster response where high rates ofline scan are required. It is therefore the primary object of thepresent invention to provide an image dissector tube utilizing bothmagnetic focusing and electrostatic deflection for line scanning toprovide a more efficient structure with improved operatingcharacteristics.

These results are achieved by a novel tube structure which utilizesmagnetic focusing coils extending axially around the tube envelopebetween the photocathode at one end and electron multiplier at the otherend, one set of magnetic deflection coils around the front portion ofthe tube between the photocathode and a first transverse apertured plateto provide vertical deflection for the slower frame scan, and a pair ofhorizontally extending electrostatic deflection plates between the firstapertured plate and a second transverse apertured plate adjacent theelectron multiplier to provide horizontal deflection for high speed linescan. The effects of the focusing coil establishing an axial magneticfield and the horizontally positioned electrostatic plates forming anelectrostatic field in the vertical direction combine to cause acycloidal trajectory of the electrons which provides the horizontalscanning of the electron image across the second aperture. The firstaperture is in the form of a horizontal slit t provide sharp resolutionin the vertical dimension for the image scanned by the verticaldeflection coils. The second aperture is in the form of a vertical slitto provide sharp resolution in the horizontal dimension and tocompensate for phase shift or displacement in the vertical directioncaused by the length of the electrostatic plates not corre- "icesponding exactly to an integral number of focusing loops between the twoapertures. The details of the invention will be more fully understoodand other objects and advantages will become apparent in the followingdescription and accompanying drawings wherein:

FIG. 1 shows a three-dimensional sectional schematic view of the noveltube structure;

FIG. 2 shows a three-dimensional view of a curve of the electron pathunder the influence of magnetic focusing and electrostatic deflectionfields, and

FIG. 3 shows a schematic of the relationship of the electron image fromthe first aperture as scanned across the second aperture.

As shown in FIG. 1, an external image 10 or scene of varying lightintensity is projected onto a photoeathode 12 on the inner surface of aface plate at one end of a tubular envelope 14. The photocathode emitselectrons in accordance with the light image. A set of electromagneticdeflection coils 16 provides repetitive relatively slow frame scanningof the electron image in the vertical direction across a first aperture18 in a transverse plate 20. Aperture 18 is in the form of a narrowhorizontal slit with a small vertical dimension to provide a fine limitfor resolution in the vertical direction. Electrons passing throughaperture 18 are subjected to an electrostatic field E as indicated inFIG. 2, in the vertical direction, established by a pair of horizontalpreferably concave deflection plates 22 extending along and outwardlycurved from the longitudinal axis of the tube. At the same time theelectrons are affected by the axial magnetic field B from focusing coils24. As is well known, the cross field relationship established by thetwo interacting orthogonal fields in the Y and Z directions, causes theelectrons to follow a cycloidal curve having a resultant vector alongthe X axis which provides scanning in the X direction. For integralscanning cycles the X axis deflection is at right angles to theelectrostatic deflection field B The basic theory and mathematicalrelationships of this electron trajectory may be found in the textentitled Electron Optics, by O. Klemper, published in 1953 by CambridgeUniversity Press. The usual sawtooth scanning voltage varying about afixed direct voltage level is applied to the deflection plates andsuitable potentials between the photocathode and first apertured plateprovide initial electron acceleration along the tube length. A fieldmesh (not shown) spaced closely to the cathode may also provideacceleration.

The length of the plates along the tube axis represents a compromisebetween plate capacitance, which increases with size and limits the rateof scan, and deflection sensitivity, which decreases with shorter platessince higher voltages are required. The plates may extend only a shortdistance from the first aperture 18 but, for maximum sensitivity andresolution, preferably extend to a second aperture plate 26 adjacent anelectron multiplier 28. The separation of the plates in the verticaldimension along each point of the tube axis is determined by the samecycloidal curve of FIG. 2 which provides the scan in the horizontal or Xdirection. The Y dimension between the plates is thus preferably twicethe intantaneous maximum displacement from the axis to the curve at eachpoint to form a pair of curved plates symmetrically positioned about thelongitudinal axis. The plates diverge from a small dimension adjacentthe horizontal edges of the first aperture to a larger separation at thecentral portion and then converge at the other end. For best deflectionsensitivity and to avoid fringe field problems, it is preferable toconverge the deflection plates at both ends as shown, with an outwardlycurved structure opposite to that of conventional deflection platecurvature.

The separation of the apertured plates and cathode is determined by thefocusing requirement that there be an integral number of focusing loopsbetween the photocathode and first apertured plate and between the twoapertures. The two apertured plates are preferably connected to the samepotential. Due to inherent nonuniformities in the deflection fields andthe physical limitation that the deflection plates cannot extend exactlyto the full length between apertures, a phase shift or displacement inthe vertical direction occurs, as illustrated in FIG. 3. The electronimage 30 from aperture 18, shown in dashed lines, thus scans acrossaperture 32 in both the horizontal and vertical directions. In order tocompensate for this phase shift or vertical displacement, aperture 32 isextended to form a vertical slit with a narrow dimension a'x along theedge in the horizontal direction to define X axis resolution. The Ydimension of aperture 32 must be long enough to accommodate the entireimage of the first aperture as it is scanned in the nonorthogonaldirection at an angle with respect to the horizontal line. In addition,the curved deflection plates must have a wider separation at the endadjacent transverse plate 26 and the electron multiplier to accommodatethe full length of aperture 32. The first dynode of the electronmultiplier must also be of sufficient length and positive voltage withrespect to the photocathode to receive all of the electrons passingthrough aperture 32. The output signal is further amplified in themultiplier, with suitable potentials between the various dynodes andthen applied to any suitable utilization device.

In some cases where vertical scan is provided externally, such as bymovement of the vehicle carrying the image tube, the vertical deflectioncoils may be omitted. The first horizontal aperture is then replaced bya limited area photocathode with electrons being scanned and acceleratedacross the second aperture in the same manner as previously described.

The present invention thus provides a novel, compact, fast acting imagedissector of high resolution. While only a single embodiment has beenillustrated, the invention is not be considered as limited to the exactform or use shown and many variations may be made in the particularconfiguration without departing from the scope of the invention as setforth in the appended claims.

What is claimed is:

1. An image dissector tube comprising:

a tubular envelope;

a photocathode at one end of said envelope;

means projecting an image of variable light intensity onto saidphotocathode, said photocathode providing an electron imagecorresponding to said light image;

a first apertured plate spaced from said photocathode along thelongitudinal axis of said tube and positioned transversely with respectto said axis, said first plate having an aperture with a narrowdimension in the vertical direction and a long dimension in thehorizontal direction;

means scanning the electron image across said first aperture in thevertical direction;

a second apertured plate spaced from said first plate along saidlongitudinal axis and having a second aperture therein;

a pair of horizontally positioned electrostatic deflection platesextending longitudinally between said first and second apertured platesproviding an electrostatic deflection field in the vertical direction,said electrostatic deflection plates being concave to said longitudinalaxis and converging at each end adjacent the horizontal edges of saidapertures;

electromagnetic means extending axially around said tube envelopeproviding a magnetic field for focusing said electron image along thelongitudinal axis, said electrostatic and magnetic fields providinghorizontal line scanning of said electron image across said secondaperture; and

an electron multiplier positioned at the other end of said tube adjacentsaid second aperture providing an output signal in accordance with theelectrons passing through said second aperture.

2. The device of claim 1 wherein said second aperture has a narrowdimension in the horizontal direction and a long dimension in thevertical direction.

3. The device of claim 1 wherein the curved plates conform to acycloidal electron trajectory resulting from the interaction of themagnetic focusing and electrostatic deflection fields.

4. The device of claim 1 wherein said electromagnetic focusing meansextends from said photocathode to said second apertured plate.

5. The device of claim 4 wherein said means scanning said electron imagein the vertical direction comprises electromagnetic coils extendingaxially around said tube envelope between said photocathode and firstapertured plate.

6. The device of claim 5 wherein said first and second apertured platesare positioned at integral numbers of focusing loops along said tube.

References Cited UNITED STATES PATENTS 2,152,820 4/ 1939 Schlesinger313-79 X 2,213,176 8/1940 Rose 313-79 2,266,621 12/1941 De Vore 31379 X2,377,972 6/ 1945 Schade 31367 X 3,225,237 12/ 1965 Cope 313- ROBERTSEGAL, Primary Examiner.

US. Cl. X.R. 313-80

